Messages in this thread Patch in this message | | | From | Chen Yu <> | Subject | [PATCH v3 1/2] sched/fair: Introduce short duration task check | Date | Thu, 1 Dec 2022 16:44:08 +0800 |
| |
Introduce short-duration task checks, as there is requirement to leverage this attribute for better task placement.
There are several choices of metrics that could be used to indicate if a task is a short-duration task.
At first thought the (p->se.sum_exec_runtime / p->nvcsw) could be used to measure the task duration. However, the history long past was factored too heavily in such a formula. Ideally, the old activity should decay and not affect the current status too much.
Although something based on PELT could be used, se.util_avg might not be appropriate to describe the task duration: 1. Task p1 and task p2 are doing frequent ping-pong scheduling on one CPU, both p1 and p2 have a short duration, but the util_avg can be up to 50%. 2. Suppose a task lasting less than 4ms is regarded as a short task. If task p3 runs for 6ms and sleeps for 32ms, p3 should not be a short-duration task. However, PELT would decay p3's accumulated running time from 6ms to 3ms, because 32ms is the half-life in PELT. As a result, p3 would be incorrectly treated as a short task.
It was found that there was once a similar feature to track the duration of a task, which is in Commit ad4b78bbcbab ("sched: Add new wakeup preemption mode: WAKEUP_RUNNING"). Unfortunately, it was reverted because it was an experiment. So pick the patch up again, by recording the average duration when a task voluntarily switches out. Introduce SIS_SHORT to control this strategy.
The threshold of short duration reuses sysctl_sched_min_granularity, so it can be tuned by the user. Ideally there should be a dedicated parameter for the threshold, but that might introduce complexity.
Suggested-by: Tim Chen <tim.c.chen@intel.com> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Chen Yu <yu.c.chen@intel.com> --- include/linux/sched.h | 4 ++++ kernel/sched/core.c | 2 ++ kernel/sched/fair.c | 17 +++++++++++++++++ kernel/sched/features.h | 1 + 4 files changed, 24 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h index ffb6eb55cd13..64b7acb77a11 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -558,6 +558,10 @@ struct sched_entity { u64 nr_migrations; + u64 prev_sum_exec_runtime_vol; + /* average duration of a task */ + u64 dur_avg; + #ifdef CONFIG_FAIR_GROUP_SCHED int depth; struct sched_entity *parent; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index daff72f00385..c5202f1be3f7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4348,6 +4348,8 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) p->se.prev_sum_exec_runtime = 0; p->se.nr_migrations = 0; p->se.vruntime = 0; + p->se.dur_avg = 0; + p->se.prev_sum_exec_runtime_vol = 0; INIT_LIST_HEAD(&p->se.group_node); #ifdef CONFIG_FAIR_GROUP_SCHED diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e4a0b8bd941c..a4b314b664f8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6200,6 +6200,16 @@ static int wake_wide(struct task_struct *p) return 1; } +/* + * If a task switches in and then voluntarily relinquishes the + * CPU quickly, it is regarded as a short duration task. + */ +static inline int is_short_task(struct task_struct *p) +{ + return sched_feat(SIS_SHORT) && + (p->se.dur_avg <= sysctl_sched_min_granularity); +} + /* * The purpose of wake_affine() is to quickly determine on which CPU we can run * soonest. For the purpose of speed we only consider the waking and previous @@ -7680,6 +7690,13 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev) struct sched_entity *se = &prev->se; struct cfs_rq *cfs_rq; + if (sched_feat(SIS_SHORT) && !prev->on_rq) { + u64 this_dur = se->sum_exec_runtime - se->prev_sum_exec_runtime_vol; + + se->prev_sum_exec_runtime_vol = se->sum_exec_runtime; + update_avg(&se->dur_avg, this_dur); + } + for_each_sched_entity(se) { cfs_rq = cfs_rq_of(se); put_prev_entity(cfs_rq, se); diff --git a/kernel/sched/features.h b/kernel/sched/features.h index ee7f23c76bd3..efdc29c42161 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -62,6 +62,7 @@ SCHED_FEAT(TTWU_QUEUE, true) */ SCHED_FEAT(SIS_PROP, false) SCHED_FEAT(SIS_UTIL, true) +SCHED_FEAT(SIS_SHORT, true) /* * Issue a WARN when we do multiple update_rq_clock() calls -- 2.25.1
| |